Mixtures of thiophosphates, oxygen phosphates and pyrophosphates

ABSTRACT

Mixtures of Thiophosphates, pyrophosphates containing both oxygen and sulfur, and oxygen phosphates are effective as corrosion inhibitors particularly in aqueous and/or oxygenated systems. The mixtures are synergistically more effective as corrosion inhibitors than each component individually. These synergistic mixtures are also effective for other uses such as for scale preventatives, etc.

United States Patent 1191 Redmore et a1.

[4 1 Sept. 30, 1975 1 MIXTURES OF THIOPHOSPHATES, OXYGEN PHOSPHATES ANDPYROPHOSPHATES [75] Inventors: Derek Redmore, St. Louis; Alfred E.

Woodson, Festus, both of Mo.

[73] Assignee: Petrolite Corporation, St. Louis,

[22] Filed: July 17, 1972 [21] Appl. No.: 272,626

[56] References Cited UNITED STATES PATENTS 2,344,395 3/1944 Cook et all252/389 X 2,579,038 12/1951 Evans et 111.. 252/466 2,742,369 4/1956Hatch 252/389 X 2,900,222 8/1959 Kahler et a1. 252/387 3,004,056 10/1961Nunn et a1. 260/950 X 3,033,889 5/1962 Chiddix et a1. 252/389 X3,337,654 8/1967 Cyba 260/950 3,462,365 8/1969 Vogelsang 252/180 X3,488,289 1/1970 Tate .1 252/180 3,489,682 1/1970 Lesuer 252/389 X3,510,436 5/1970 Silverstein et a1. 252/389 X 3,533,943 10/1970 Papay252/389 X 3,597,352 8/1971 Stanford et 211 252/180 X 3,654,170 4/1972Woodson 1 1 252/181 3,668,138 6/1972 Hoover et a1. 252/389 X PrimaryExaminer-Herbert B. Guynn Attorney, Agent, or Firm-Sidney B. Ring; HymanF. Glass [5 7 ABSTRACT Mixtures of Thiophosphates, pyrophosphatescontaining both oxygen and sulfur, and oxygen phosphates are effectiveas corrosion inhibitors particularly in aqueous and/or oxygenatedsystems. The mixtures are synergistically more effective as corrosioninhibitors than each component individually.

These synergistic mixtures are also effective for other uses such as forscale preventatives, etc.

8 Claims, No Drawings MIXTURES OF THIOPHOSPHATES, OXYGEN PHOSPHATES ANDPYROPHOSPHATES One of the mostdifficult problems in the field ofcorrosion inhibition is thatof preventing and/or inhibiting corrosion inoxygenated aqueous systems such as in water floods, cooling towers,drilling muds, air drilling, auto radiator systems, etc."

Many corrosion inhibitors capable of performing in non-aqueous systemsand/or non-oxygenated systems perform poorly in aqueous and/oroxygenated systems (i.e. aerobic systems).

In Application Ser. No. 821,144, filed May 1, 1969, there is describedand claimed dithiophosphoric acids and the use thereof as corrosioninhibitors in aqueous and/or oxygenated systems.

Although the reaction of simple alcohols with P S primarily proceedsaccording to the following equation I? (R)-1P'SH initially formed fromsuch alcohols yields through anhydride formation and/or isomerizationpyrophosphates as illustrated in the following equations:

Although the ratio of products will vary with reactants, properties,reaction conditions, etc., a typical reaction product ratio of productsformed by reacting an oxyalkylated alcohol with P S is as follows:

Thus, the major part of the product comprises anhydrides and/orisomerized anhydrides (i.e., pyrophosphates) which are excellentcorrosion inhibitors, etc.

The production of pyrophosphates which contain both sulfur and oxygen ofthe formula where X O or S in substantial amounts is unexpected sincethe reaction of simple alcohols, such as lower alkyl alcohols ROI-l,with P 5 yields little, if any, pyrophosphates. See l-Iouben-Weyl,Phosphorus Compounds,- Part II', p'. 684, published by Georg ThiemeVerlag in 1964. In contrast where the more complex alcohols arereacted,-for example, oxyalkylated alcohols such as of the formulaR(OA),,OI-I where R is alkyl, cycloalkyl, alkenyl, aryl, aralkyl,alkaryl, heterocyclic, etc., higher alkyl alcohols such as where R hasat least seven carbon atoms, etc., pyrophosphates comprise a substantialpart of the .resultant reaction product. In general, the yield ofpyrophosphate is increased by prolonged heating. Thus, in order toincrease'the yield of pyrophosphates, in contrast to reaction time of 13 hours for the dialkyl dithiophosphates, reaction times at elevatedtemperatures of more than 3 hours, such as 3 15 or more hours, enhancethe yield of pyrophosphates. The use of vacuum or reduced pressureduring this heating period also enhances the yield of pyrophosphates,e.g., 20 mm 150 mm.

The general procedure for reacting alcohols with P 5 to formdithiophosphoric acids is to continue reac tion until most of the P Shas dissolved and the evolution of H 5 has subsided. In contrast, thegeneral procedure for preparing the pyrophosphates is to continue thereaction past this point so as to shift the equilibrium in favor ofconverting the dithiophosphoric acids to the pyrophosphate.

Since the crude reaction products contain 0,0,- disubstituteddithiophosphoric acids ll (RO)2PSH salts of these can also be prepared.

The salts are prepared by the simple neutralization of the acid with asuitable'salt-forming base or by double decomposition. The salt moietymay be for example, Cu, Ni, Al, Pb, Hg, Cd, Sn, Zn, Mg, Na, K, NI-Iamine, C0, Sr, Ba, etc. These may be prepared from the correspondingoxide, hydroxide, carbonate, sulfide, etc. An alternative to thepreparation of salts is to use a simple combination of dithiophosphatewith a metal salt such as zinc chloride, zinc sulfate, etc. This allowsthe use of higher stoichiometric amounts of metal ions todithiophosphate, such as from 1:1 to 4:1.

The alcohols employed to prepare the ester may be oxyalkylated alcoholsfor example of the formula R(OA),, OH where CA is a moiety derived froman alkylene oxide and n is a number for example from about 1 or more,for example from 1 50, such as from 1 25, but preferably from 1 10.

The alkylene oxides employed herein are alkylene oxides of the formulawhere R,, R R and R are selected by the group consisting of hydrogen,aliphatic, cycloaliphatic, aralkyl, etc. for example ethylene oxide,propylene oxide, butylene oxide, amylene oxide, octylene oxide, styreneoxide, methyl styrene oxide, cyclohexene oxide (where R and R are joinedto make a ring), etc.

The alkylene oxide may be added to form homo polymer, stepwise to formblock polymers, as mixtures to form heteropolymers or combinationsthereof, etc. For example R(OEt-OPr),,Ol-l, etc. mixed These phosphatesderived from P 3 are designated in the following discussion as Type A.These materials are significantly improved as corrosion inhibitors andscale inhibitors by mixing with non-sulfur containing phosphatesdesignated as Type B.

The type B phosphates preferredly are formed by phosphorylation of thealcohols described above: using reagents as phosphorus pentoxide, polyphosphoric acid, phosphorus oxychloride, etc.

Examples 1 5 illustrate the thiophosphate materials and Examples 6 14the non-sulfur containing phosphate esters.

The reaction of alcohols with P is carried out in the conventionalmanner. lt may be summarized by the following idealized equation ORand/or HO-PIIL-OR In general, the alcohols employed in preparing theoxygen phosphates are the same as that employed with the thiophosphates.

The following examples illustrate thiophosphate compounds: (Type A)EXAMPLE 1 EXAMPLE 2 The alcohol derived from the addition of 1 weight ofethylene oxide to Alfol 8 10 (288g; 1 mole) was stirred at C. while P S(55g; 0.25 mole) was added in 60 mins. The reaction mixture was heatedat 100 110 under reduced pressure (75 mm) for 8 hours as H 8 wasevolved. The resulting acid was neutralized with dimethyl aniline.

EXAMPLE 3 The alcohol derived from the addition of 2 weights of ethyleneoxide to Alfol 8 l0 (432g; 1 mole) was stirred at 70 75 C. during theaddition of P S (55g; 0.25 mole). The addition was complete in 60 min.and heating was continued at 100 110 for 10 hours to complete H 8evolution. Neutralization was effected by the addition of anhydrousammonia.

The following examples use higher P 8 ratios.

EXAMPLE 4 The alcohol derived from the addition of 1 weight of ethyleneoxide to Alfol 8 10 (288g; 1 mole) was heated at 75 C while P 8 (70g;0.315 mole) was added during 45 min. The mixture was heated at C. for 3hours at which time H S evolution was complete. After cooling to 70tributylamine (42g) was added and the mixture stirred at 70 75 for 1hour to complete neutralization.

EXAMPLE 5 EXAMPLE 6 To the alcohol derived from the addition of 0.8

weight of ethylene oxide to Alfol" 8 10 (180g; 0.7 mole) was carefullyadded phosphorus pentoxide (33g; 0.23 mole). The reaction mixturespontaneously rose to 90 upon this addition. The reaction was completedby heating at C. for 1 hour to yield a straw colored liquid.

EXAMPLE 7 To the alcohol derived from Z-ethylhexanol with 1 weight ofethylene oxide added (g; 1 mole) was added phosphorus pentoxide (47g;0.33 mole) during 10 mins. This addition resulted in an exotherm takingthe temperature to 75. The phosphorylation was completed by heating at 110 for l-Vz hours yielding a pale yellow liquid.

EXAMPLE 8 To the alcohol derived from the addition of 1 weight ofethylene oxide to Alfol 8 10 (130g; 0.45 mole) was added polyphosphoricacid (77g; 0.45 mole) in 15 mins. This addition resulted in atemperature increase to 70. The reaction was then heated at 1 10 1 12for 1 hour to complete the reaction. The product was a viscous amberliquid.

The following tables present additional illustrative examples:

Example Phosphorylating No. Alcohol Reagent Procedure 9 Alfol8l0+l PExample 6 weight EtO* Alfoll4+0.5 P 0 Example 6 weight EtO l lAlfol"8l0+0.8 Polyphosphoric Example 8 weight EtO Acid 12 Alfoll4+0.5Polyphosphoric Example 8 weight EtO Acid 13 Alfol"8l0 P 0 Example 6 l42-ethyl hexanol P 0 Example 6 Alfol" linear alcohols number indicatespredominant carbon chain.

E0 Ethylene ()xide The weight ratio of thiophosphate and/or pyrophosphate to phosphate can vary widely'for example from about 10:1 to 1:10,such as from about 5:1 to 1:5 for example from about 3:1 to 1:3, butpreferably from about 2:1 to 1:2.

In addition we have discovered that the presence of zinc in thecompositions of this invention further enhances the synergism of thethio and non-thio phosphates and pyrophosphates of this invention. Zincis employed in amounts from about 0.5 to 50% by weight based on theactive ingredients, such as from about 1 to 40 for example preferablyfrom about 5 to USE IN BRINES This phase of the invention relates to theprevention of corrosion in systems containing a corrosive aqueousmedium, and most particularly in systems containing brines.

More particularly, this invention relates to the prevention of corrosionin the secondary recovery of petroleum by water flooding and in thedisposal of waste water and brine from oil and gas wells. Still moreparticularly, this invention relates to a process of prevent ingcorrosion in water flooding and in the disposal of waste water and brinefrom oil and gas wells which'is characterized by injecting into anunderground formation an aqueous solution containing minor amountsofcompositions of this invention, in sufficient amounts to prevent thecorrosion of metals employed in such operation. This invention alsorelates to corrosion inhibited brine solutions of these compounds/ Whenan oil well ceases to flow by the natural pressure in the formationand/or substantial quantities of oil can no longer be obtained by theusual pumping methods, various processes are sometimes used for thetreatment of the oil-bearing formation in order to increase the flow ofthe oil. These processes are usually de' scribed as secondary recoveryprocesses. One such process which is used quite frequently is the waterflooding process wherein water is pumped under pressure into what iscalled an injection well and oilalong with quantities of water, thathave been displaced from the formation, are pumped out of an adjacentwell usually referred to as a producing well. The oil which is pumpedfrom the producing well is then separated from the water that has beenpumped from the producing system. If the water is recirculated in aclosed system without substantial aeration, the secondary recoverymethod is referred to herein as a closed water flooding system.

Because of the corrosive nature of oil field brines, to economicallyproduce oil by water flooding, it is necessary to prevent or reducecorrosion since corrosion increases the cost thereof by making itnecessary to repair and replace such equipment at frequent intervals.

We have now discovered a method of preventing corrosion in systemscontaining a corrosive aqueous media, and most particularly in systemscontaining brines, which is characterized by employing the compositionsof this invention.

We have also discovered an improved process of protecting from corrosionmetallic equipment employed in secondary oil recovery by water floodingsuch as injection wells, transmission lines, filters, meters, storagetanks, and other metallic implements employed therein and particularlythose containing iron, steel, and ferrous alloys, suchprocess beingcharacterized by em- In many oil fields large volumes of water areproduced and must be disposed of where water flooding" operations arenot in use or where flooding operations f cannot handle the amount ofproduced water. Most States have laws restricting pollution of streamsand land with produced waters, and oil producers must then find somemethod of disposing of the waste produced salt water. In many instancestherefore, the salt water is disposed of by injecting the water intopermeable low' pressure strata below the fresh water level. Theformation into which the water is injected is not the oil producingformation and this type of disposal is defined as salt water disposal orwaste water disposal. The problems of corrosion of equipment areanalogous to those encountered in the secondary recovery operation bywater flooding.

The compositions of this invention can also be used in such waterdisposal wells thus providing a simple and economical method of solvingthe corrosion problems encountered in disposing of unwanted water.

Water flood and waste disposal operations are too well known to requirefurther elaboration. In essence, in the present process, the floodingoperation is effected in the conventional manner except that theflooding medium contains a minor amount of the reducing compound,sufficient to prevent corrosion, in

concentrations of about 10 p.p.m. to 10,000 p.p.m., or

more, for example, about 50 to 5000 p.p.m., but preferably about l5 to1,500 p.p.m. The upper limiting amountof the compounds is determined byeconomic considerations. Since the success of a water flooding operationmanifestly depends upon its total cost being less than the value of theadditional oil recovered from the oil reservoir, it is quite importantto use as little as possible of these compounds consistent with optimumcorrosion inhibition. Optimum performance is generally obtainedemployingabout p.p.m. Since these compounds are themselves inexpensive and areused in low concentrations, they enhance the success of a floodoperation by lowering the cost thereof.

In addition, these compounds are not sensitive to oxygen content of thewater and these are effective corrosion inhibitors in both open waterflooding systems and closed water flooding systems.

While the flooding medium employed in accordance with the presentinvention contains water or oil field brine and the compounds, themedium may also contain other materials. For example, the floodingmedium may also contain other agents such as surface active agents ordetergents which aid in wetting throughout the system and also promotethe desorption of residual oil from the formation, sequestering agentswhich prevent the deposition of calcium and/or magnesium compounds inthe interstices of the formation, bactericides which prevent theformation from becoming plugged through bacterial growth, tracers, etc.Similarly, they may be employed in conjunction with any of the operatingtechniques commonly employed in water flooding and water disposalprocesses, for example five spot flooding, peripheral flooding, etc.,and in conjunction with other secondary recovery methods.

USE IN FLUIDS FOR DRILLING WELLS This phase of the invention relates tothe use of the compounds of this invention as corrosion inhibitors inproducing an improved drilling fluid useful in drilling oil and gaswells.

Fluids commonly used for the drilling of oil and gas wells are of twogeneral types: water-base drilling fluids comprising, for example, aclay suspended in water, and oil-base drilling fluids comprising, forexample, a clay or calcium carbonate suspended in mineral oil.

A third type of drilling fluid which has recently been developed, is oneof oil-in-water or water-in-oil emulsion, for example, emulsions ofmineral oil in water or water in mineral oil formed by means ofemulsifiers such as sulfuric acid; Turkey-red oil; soaps of fatty acidsfor example, sodium oleate; emulsoid colloids, for example starch,sodium alginate, etc. Varying amounts of finely divided clay, silica,calcium carbonate, blown asphalt and other materials may be added tothese emulsions to improve their properties and control their weight.

We have discovered that the compositions of this invention can beemployed as a corrosion inhibitor in drilling fluids.

USE IN AIR DRILLING It has long been conventional practice in drillingdeep bore holes to circulate a drilling mud down through the drill stemand up through the bore hole between the wall of the bore hole and thedrill stem for the removal of chips or cuttings from the bore hold andto provide support for the wall of the bore hole. More recently, in thedrilling of holes in which wall support provided by drilling mud is notemployed, drilling has been carried out with the use of air for chipremoval. Such drilling is not only normally faster than mud drilling butis indispensable in areas where the supply of water is limited or whendrilling through cavernous formations into which the drilling mud flowsand becomes lost.

The increasing popularity of air or gas drilling has come about not onlybecause this method of drilling is frequently faster, as noted above,but for the additional reasons that the drill bits last longer, theprovision and handling of water under wide ranges of temperatureconditions is avoided, boring samples are easily observed when they arenot mixed with mud, and there is no loss involved as in the case of muddrilling when drilling through cavernous formations. Furthermore, promptremoval of water entering the hole maintains a dry hole and thelikelihood of wall collapse is thereby reduced.

In a typical air drilling operation there may be provided, for example,an up-flow of air in the bore hole having a velocity of the order of3,000 feet per minute. This flow of air upwardly through the bore hole,which is produced by air pumped downwardly through the drill stem,provides adequate removal of cuttings. The air is delivered to the drillstem at pressures of 20 to 60 lbs. per square inch and for dewatering orfor breaking obstructions, as will be hereinafter-described, thepressures may be increased to to 200 lbs. or more per square inch.

Air drilling operations are frequently hampered by the inflow of waterinto the bore hole when the drill bit is penetrating a water bearingstratum or when the bore hole has passed through a water bearing stratumthat has not been cased. Normally, if drilling proceeds uninterruptedlyboth before and during penetration into a water bearing stratum, theflow of air is sufficient to blow the water out of the bore hole alongwith the cuttings and drilling dirt. There are, however, two majorproblems encountered in air drilling when water is entering the borehole. The first problem occurs when there is a small inflow of watersufficient to cause a dampening of the cuttings which, under certainconditions, will then ball-up, clogging and sometimes jamming the drillbit. The second problem is encountered when there is a substantialamount of water remaining in the bottom of the bore hole during drillingcausing a sloughing of the side wall of the bore hole. This lattercondition may arise even though the water entering the bore hole isbeing blown out of the hole as fast as it enters. If there is asubstantial inflow of water or if there is a substantial flow of waterpast a region of the bore hole susceptible to this condition, the waterpassing that region of the bore hole may cause a sloughing of the sidewall.

The addition of foam forming materials to the air flow when air drillingis employed in conjunction with sufficient water to provide foaminggives rise to numerous advantages in drilling operations. The water maybe introduced either through a water bearing stratum being penetrated bythe drill bit or, alternatively, if the hole is dry, water may beintroduced from the surface of the earth through the drill stem inconjunction with the delivery of compressed air and foam formingmaterial .through the drill stem to the drill bit. In either case thewater may be said to be existing in the bore hole, and drillingoperations are described in US. Pat. No. 3,130,798.

The compositions of this invention can be employed as a corrosioninhibitor in a drilling system.

The compositions of this invention may also be added to other aqueousand/or oxygenated systems such as steam generating systems, watercirculating systems such as in cooling towers, in automobile radiators,in diesel locomotive engines, in boiler water, sea-water ship ballast,etc.

The amount of-the compositions of the invention to be employed as acorrosion inhibitor can vary widely depending upon particularcompounds,-the particular" system, the amounts of owygen present, etc.We may employ concentrations of from about 0.5 to 5,000 p.p.m., such asfrom about 4 to 4,000 p.p.m., for example from about 20 to 2,000 p.p.m.,but preferably from about 100 to l,000p.p.m. The optimum amount, to bedetermined in each instance, which will depend on function andeconomics, can be lesser or greater than the above amounts under properconditions.

use in COOLING TOWERS The compositions of this invention can also beemployed in cooling towers since they are particularly effective ininhibiting corrosion in such systems. This is illustrated by thefollowing examples.

Corrosion Tests Corrosion tests weremade using sand blasted 1020 mildsteel coupons monitored by a polarization resis-- Sodium bicarbonate 2.9g Magnesium sulfate 57 g Calcium chloride 5.2 g Calcium sulfate 7.2 gSodium sulfate 8.3 g

made up to'5 gallons with deionized water Composition designated 1X ismade diluting 1 part 10X to 10 parts. Protection is calculated in theusual manner from'cor rosion rate (R) of fluids without inhibitors andcorrosion rate (R in presence of a particular inhibitor according to theformula:

X 100 "/1 protection Table 1 below shows the inhibitor performance ofthe thio phosphate compositions (Type A).

Table l Concentration Water Com Protection Protection Inhibitor p.p.m.position 8 hrs. 24 hrs.

Example l 25 IX l% Example 4 A 50 IX 30% 30% Exam le I 100 lOX 20% 37%Example 4 100 X 18% 47% Table 2 shows the inhibitor performance ofnon-sulfur containing phosphate compositions (Type B).

Table 2 Concentration Water C om- Protection Protection Inhibitor p.p.m.position 8 hrs. 24 hrs.

Example 6 50 1x 7I% l7% Example 6 100 1X 78% 63% Example 8 50 IX 51% 58%Example 8 100 1X 60% 52% Example 9 50 1X 80% 13% Example 9 100 1X 86%87% Example 1 l 100 IX 36% 34% Example ll lOO 10X 41% 33% Example I4 10010X 66% 62% Table 3 shows the synergistic behaviour of mixtures of thecompositions of Type A and Type B as corrosion inhibitors.

Table 3 Inhibitor Combination Water Protection Composi at Type B(p.p.m.) Type A (p.p.m.) tion 8 hrs. 24 hrs.

Example ll (66) Example 1 (33) 1X 86% 89% Example ll (33) Example l (16)1X 77% Example ll Example I (25) IX 89% 87% Example ll (50 Example I(50) 1X 97% 96% Example ll (80) Example I (20) IX 93% Example 6 (66)Example I (33) IX 83% 85% Example 9 (66) Example I (33) IX 8l% 93%Example ll (66) Example 4 (33) lX 80% 91% Example ll (75) Example I (25)10X 86% 9l% Example ll (66) Example l (33) 10X 87% 90% Example ll (80)Example I (20) 10X 85% 96% Example 6 (66) Example l (33) l0X 40% Example9 (66) Example I (33) lOX 43% Example ll (75) Example 4 (25) 10X 75% 82%Example 6 (75) Example 4 (25) lOX 60% 81% Table 4 shows that theaddition of zinc ions can exert a further synergistic effect on thecombinations of Table 3.

Table 4 Inhibitor Combination Zinc Water Protection Composiat Type B(p.p.m.) Type A (p.p.m.) p.p.m. tion 8 24 hrs. hrs.

Example ll (60) Example I (30) 10 1X 77% 68% Example ll (50) Example I(25) 25 IX 88% 92% Example ll (60) Example I (30) I0 10X 98% I007:Example ll (50) Example I (25) 25 10X 98% 99% USE AS SCALE INHIBITORSMost commercial water contains alkaline earth metal cations, such ascalcium, barium, magnesium, etc., and

anions such as bicarbonate, carbonate, sulfate, oxalate,

ble compounds with the ions alreay present in the solution.

As these reaction products precipitate on the surfaces of thewater-carrying system, they form scale. The scale prevents effectiveheat transfer, interferes with fluid flow, facilitates corrosiveprocesses, and harbors bacteria. Scale is an expensive problem in manyindustrial water systems, causing delays and shutdowns for cleaning andremoval.

Scale-forming compounds can be prevented from precipitating byinactivating their cations with chelating of sequestering agents, sothat the solubility of their reaction products is not exceeded.Generally, this approach requires many times as much chelating orsequestering agent as cation present, and the useof large amounts oftreating agent is seldom desirable or economical.

More than twenty-five years ago it was discovered that certain inorganicpolyphosphates would prevent such precipitation when added in amountsfar less than the concentrations needed for sequestering or chelating.See, for example, Hatch and Rice, Industrial Engineering Chemistry, Vol.3 l p. 51, at 53; Reitemeir and Buchrer, Reitemeier Journal of PhysicalChemistry, vol. 44, No. 5, p. 535 at 536 (May 1940); Pink and RichardsonU.S. Pat. No. 2,358,222; and Hatch U.S. Pat. No. 2,539,305. When aprecipitation inhibitor is present in a potentially scale-forming systemat a markedly lower concentration than that required for sequesteringthe scale forming cation, it is said to be present in threshold amounts.Generally, sequestering takes place at a weight ratio of thresholdactive compound to scale-forming cation component of greater than aboutten to one, and threshold inhibition generally takes place at a weightration of threshold active compound to scale-forming cation component ofless than about 0.5 to l.

The threshold concentration range can be demonstrated in the followingmanner. When a typical scaleforming solution containing the cation of arelatively insoluble compound is added to a solution containing theanion of the relatively insoluble compound and a very small amount of athreshold active inhibitor, the relatively insoluble compound will notprecipitate even when its normal equilibrium concentration has beenexceeded. If more of the threshold active compound is added, aconcentration is reached where turbidity or a precipitate or uncertaincomposition results. As still more of the threshold active compound isadded, the solution again becomes clear. This is due to the fact thatthreshold active compounds in high concentrations also act assequestering agents, although sequestering agents are not necessarilythreshold compounds. Thus, there is an intermediate zone between thehigh concentrations at which threshold active compounds sequester thecations of relatively insoluble compounds and the low concentrations atwhich they act as threshold inhibitors. Therefore, one could also definethreshold concentrations as all concentrations of threshold activecompounds below that concentration at which this turbid zone orprecipitate is formed. Generally the threshold active compound will beused in a weight ratio of the compound to the cation component of thescale-forming salts which does not exceed about 1.

The polyphosphates are generally effective threshold inhibitors for manyscale-forming compounds at temperatures below lF. But after prolongedperiods at higher temperatures, they lose some of their effectiveness.Moreover, in an acid solution, they revert to ineffective or lesseffective compounds.

A compound that has sequestering powers does not predictably havethreshold inhibiting properties. For example, ethylene diaminetetracetic acid salts are powerful sequesterants but have no thresholdactivities.

We have now discovered a process for inhibiting scale such as calcium,barium and magnesium carbonate, sulfate, silicate, etc., scale whichcomprises employing threshold amounts of compositions of this invention.

Scale formation from aqueous solutions containing an oxide variety ofscale forming compounds, such as calcium, barium and magnesiumcarbonate, sulfate, silicate, oxalates, phosphates, hydroxides,fluorides and the like are inhibited by the use of threshold amounts ofthe compositions of this invention which are effective in small amounts,such as less than p.p.m., and are preferably used in concentrations ofless than 25 p.p.m.

The compounds of the present invention will inhibit the deposition ofscale-forming alkaline earth metal compounds on a surface in contactwith aqueous solution of the alkaline earth metal compounds over a widetemperature range. Generally, the temperatures of the aqueous solutionwill be at least 40F, although significantly lower temperatures willoften be encountered. The preferred temperature range for inhibition ofscale deposition is from about to about 350F. The aqueous solutions orbrines requiring treatment generally contain about 50 p.p.m. to about50,000 ppm. of scale-forming salts. The compounds of the presentinvention effectively inhibit scale formation when present in an amountof from 0.1 to about 100 p.p.m., and preferably 0.2 to 25 p.p.m. whereinthe amounts of the inhibitor are based upon the total aqueous system.There does not appear to be a concentration below which the compounds ofthe present invention are totally ineffective. A very small amount ofthe scale inhibitor is effective to a correspondingly limited degree,and the threshold effect is obtained with less than 0.]

p.p.m. There is no reason to believe that this is the minimum effectiveconcentration. The scale inhibitors of the present invention areeffective in both brine, such as sea water, and acid solutions.

Calcium Scale Inhibition Test The procedure utilized to determine theeffectiveness of our scale inhibitors in regard to calcium scale is asfollows:

several 50 ml. samples of a 0.04 sodium bicarbonate solution are placedin l00 ml. bottles. To these solutions is added the inhibitor in variousknown concentrations. 50 ml. samples ofa 0.02 M CaCl solutions are thenadded.

A total hardness determination is then made on the 5050 mixtureutilizing the well known Schwarzenbach titration. The samples are placedin a water bath and heated at 180F. 10 ml. samples are taken from eachbottle at 2 and 4 hour periods. These samples are filtered throughmillipore filters and the total hardness of the filtrates are determinedby titration.

Total hardness after heating Table describes the scale inhibition testresults obtained.

TABLE 5 Inhibition of scale formation from a'CaCO solution at- 180F. for4 hours (200 p.p.m. CaCO5).

As is quite evident, other phosphates, thiophosphates and pyrophosphateswill be constantly developed which could be useful in our invention. Itis, therefore, not only impossible to attempt a comprehensive catalogueof such compositions, but to attempt to describe the invention in itsbroader aspects in terms of specific chemical names used would be toovoluminous and unnecessary since one skilled in the art could byfollowing the description of the invention herein select a usefulpyrophosphate. This invention lies in the use of suitable phosphates ofthis invention in conjunction with suitable salts where appropriate ascorrosion inhibitors in aqueous and/or oxygenated systems and theirindividual compositions are important only in the sense that theirproperties can affect this function. To precisely define each specificuseful phosphate and aqueous system in light of the present disclosurewould merely call for knowledge within the skill of the art in a manneranalogous to a mechanical engineer who prescribes in the construction ofa machine the proper materials and the proper dimensions thereof. Fromthe description in this specification and with the knowledge of achemist, one will known or deduce with confidence the applicability ofspecific phosphates suitable for this invention by applying them in theprocess set forth herein. In analogy to the case of a machine, whereinthe use of certain materials of construction or dimensions of part wouldlead to no practical useful result, various materials will be rejectedas inapplicable where others would be operative. We can obviously assumethat no one will wish to use a useless phosphate nor will be misledbecause it is possible to misapply the teachings of the presentdisclosure to do so. Thus, any phosphate or mixtures containing themthat can perform the function stated herein can be employed.

The alcohols employed in this invention are the same alcohols employedin Ser. No. 821,144 and 874,713. They are alkanols, preferablyoxyalkylated, and preferably having at least about 7 carbon atoms, forexample about 7 20 carbon atoms, but preferably having about 8 14 carbonatoms.

The preferred alcohols are Alfol alcohols which are linear alkanols.Thenumber associated with the trade mark indicates the predominantcarbon length. Thus in Alfol 8 10 the predominant carbon chain isbetween 8 and 10 carbon atoms. In Alfol 14 the predominant carbon lengthis 14. For optimum properties, these alcohols are oxyalkylat'e'd'witliabout'Or 5' 'l 0 moles of an alkylene oxide, preferably about 1' to '2'moles'of ethylene-ox'ide.

We claim: 5 1". A compositionof a mixture consisting essentially of t I.a rriixtureof different compoundsfeach having the formula II. a compoundor a mixture of compounds each hav- 15 ing the formula (ROhPSM and III.a compound or a mixture of compounds each having the formula Ho-rI* oH 0R a compound or a mixture of compounds each having the formula a mixtureof compounds having the formulae where X is oxygen or sulfur, each ofsaid different compounds in l containing both oxygen and sulfur and M ishydrogen, ammonium, dimethyl aniline or tributylamine, wherein theweight ratio l and II to I11 ranges from about 10:1 to 1:10, the mixtureof compounds I and [I being prepared by reacting an alkanol having 8 to14 carbon atoms or a mixture of said alkanols, which alkanol or alkanolsis or are oxyethylated with 05-10 moles of ethylene oxide, as R, with P5 first to form 0,0-disubstituted dithiophosphoric acid or a mixturethereof until most of the P S has dissolved and the evolution of H 8 hassubsided and then continuing the reaction to shift the equilibrium infavor of converting dithiophosphoric acid or a mixture thereof to thepyrophosphates, each of said compounds or the mixture of said compoundsIn being prepared by reacting an alkanol having 8 to 14 carbon atoms ora mixture of said alkanols, which alkanol or alkanols is oxyethylatedwith 0.5-10 moles of ethylene oxide, as R, with P 0 or polyphosphoricacid.

em in the amount of from about 1% to 40% by weight of l, 11 and lll.

7. The composition of claim 5 where said zinc is present in the amountfrom about 0.5% to by weight of l, 11 and Ill.

8. The composition of claim 5 where said zinc is present in the amountof from about 5% to 25% by weight of 1, [I and Ill.

1. A COMPOSITION OF MIXTURE CONSISTING ESSENTIALLY OF
 1. A MIXTURE OFDIFFERENT COMPOUNDS, EACH HAVING THE FORMULA
 2. The composition of claim1 where the weight ratio of I and II to III ranges from about 5:1 to1:5.
 3. The composition of claim 1 where the weight ratio of I and II toIII ranges from about 3:1 to 1:3.
 4. The composition of claim 3 wherethe weight ratio of I and II to III ranges from about 2:1 to 1:2.
 5. Thecomposition of claim 1 which also contains zinc ions.
 6. The compositionof claim 5 where said zinc is present in the amount of from about 1% to40% by weight of I, II and III.
 7. The composition of claim 5 where saidzinc is present in the amount from about 0.5% to 50% by weight of I, IIand III.
 8. The composition of claim 5 where said zinc is present in theamount of from about 5% to 25% by weight of I, II and III.
 11. ACOMPOUND OR A MIXTURE OF COMPOUNDS, EACH HAVING THE FORMULA
 111. ACOMPOUND OR A MIXTURE OF COMPOUNDS EACH HAVING THE FORMULA